黑龙江东部依兰珠山变辉长岩的年代学、地球化学及其构造意义

Geochronology and geochemistry of Zhushan metagabbro in Yilan,eastern Heilongjiang and its tectonic implication

对黑龙江东部依兰珠山变辉长岩进行了锆石年代学和地球化学研究,以确定其形成时代、成因及构造背景。变辉长岩锆石均呈自形-半自形晶,具典型的条痕状吸收特征和较高的Th/U比值(0.20~0.86),暗示其岩浆成因。LA-ICP-MS U-Pb测年结果为(256±3)Ma,表明珠山变辉长岩形成于晚二叠世。地球化学特征显示变辉长岩具有贫硅,富镁、铁、铝、钙的特征;其轻稀土元素(LREEs)和大离子亲石元素(Rb、Ba)富集,重稀土元素(HREEs)和高场强元素(Nb、Ta、Zr、Hf和Ti)亏损。结合区域地质资料,认为珠山变辉长岩为俯冲流体交代地幔楔的产物,其形成可能与古大洋板块的俯冲作用有关,暗示佳木斯地块与松嫩地块在晚二叠世之前尚未碰撞拼合。

The authors analyzed zircon geochronological data and geochemical data of Zhushan metagabbro from Yilan, eastern Heilongjiang to determine their age, petrogenesis and tectonic setting. Zircons from metagabbro are euhedral-subhedral in shape with typical striation absorption features and high Th/U ratios （0.20-0.86）, implying their magmatic origin. LA-ICP-MS zircon U-Pb dating shows that Zhushan metagabbro from Yilan formed during Late Permian with age of （256±3）Ma. The geochemical characteristics show that these metagabbros are low in silicon and high in magnesium, iron, aluminum and calcium. The rocks are enriched in LREEs and LILEs （Rb, Ba）, and depleted in HREEs and HFSEs （Nb, Ta, Zr, Hf and Ti）. Combined with the regional geological data, it is proposed that Zhushan metagabbro was derived from a mantle wedge that had been metasomatized by subducted slab-derived fluids. Its formation was probably related to the subduction of a paleo-oceanic plate, which implies that the collision between the Jiamusi Massif and the Songnen Massif may have not happened before Late Permian.